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R C Deth

Publications and source records attributed to R C Deth.

At least 19 recordsLinked to original sources
PubMed1992

Phorbol ester and staurosporine modulation of antagonist and agonist binding to alpha-2 adrenergic receptors: differential influence on Na+ versus guanylylnucleotide regulation.

The modulatory influence of the protein kinase C (PKC) activator phorbol dibutyrate (pDBu) and the PKC inhibitor staurosporine on the binding of the antagonist rauwolscine and the agonist (-)-epinephrine to alpha-2 adrenergic receptors was studied in plasma membranes from bovine aorta. In control membranes [3H]rauwolscine binding exhibited high (KDH = 110 pM) and low (KDL = 2.4 nM) affinity components. The addition of 0.1 mM 5'-guanylylimidodiphosphate [Gpp(NH)p] reduced binding to a single component (KD = 1.3 nM) and the addition of 140 mM NaCl increased the proportion of high affinity sites from 7 to 15%, whereas the combination of both Gpp(NH)p and NaCl did not differ from values for NaCl alone. PDBu pretreatment had little effect on [3H]rauwolscine binding with the exception of a small increase in KD in the presence of Gpp(NH)p. Staurosporine pretreatment, however, eliminated the high-affinity component in the absence of Gpp(NH)p or NaCl and rendered Gpp(NH)p ineffective. NaCl was able to restore two components of [3H]rauwolscine binding to the same extent as in untreated membranes. Epinephrine displaced [3H]rauwolscine in a biphasic manner (KDH = 93 nM, KDL = 3.5 microM; %RH = 42). In untreated membranes Gpp(NH)p reduced epinephrine affinity, but did not alter the %RH. NaCl alone increased KDL and caused a partial decrease in %RH, whereas the combination of Gpp(NH)p and NaCl was required to produce a single, low-affinity state (KD = 11.9 microM). PDBu pretreatment reduced epinephrine affinity and blocked the effectiveness of Gpp(NH)p, but the action of NaCl was more pronounced than in untreated membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkaloids↗
PubMed1991

Agonist-induced modulation of agonist binding to alpha 1-adrenoceptors in bovine aorta.

Prolonged exposure of tissues to hormone agonists results in a subsequent reduction in the sensitivity of the tissue through a process known as desensitization. The desensitization response, either homologous or heterologous, has been shown to be correlated with receptor phosphorylation. Recently we have provided evidence that protein kinase C, when activated by a phorbol ester, regulates alpha 1-adrenoceptor coupling to a G-protein. In the present study, the effects of epinephrine (10 microM) pretreatment on the binding behavior of the alpha 1-adrenoceptor were determined from radioligand binding assays at 25 degrees and 2 degrees C. Pretreatment of tissues with epinephrine for 25 min moderately decreased [3H]prazosin binding by 12% (Bmax 121.5 fmol/mg) in comparison to control (139.3 fmol/mg) with no change in its affinity. The second consequence of desensitization by epinephrine is a decrease in the affinity of agonist binding to alpha 1-adrenoceptors associated with uncoupling of the receptors from the G-protein. In control membranes, at 25 degrees C, epinephrine defined two different affinity states of the receptor, viz. high affinity (KDH 16.5 nM, % RH 21) and low affinity (KDL 710 nM, % RL 79). The high affinity state formed at 25 degrees C is stabilized by forming a ternary complex with a G-protein. Addition of guanylylimidodiphosphate (Gpp(NH)p) reduced the stability of this complex resulting in a loss of high affinity sites in control membranes. On the other hand, epinephrine treated membranes exhibited only a single class of low affinity agonist binding (KDH 659 nM) and further, Gpp(NH)p had no significant effect on binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Agonists↗
PubMed1990

Developmental changes in alpha 1-adrenoceptor coupling to G-protein in bovine aorta.

Differences in epinephrine binding to alpha 1-adrenoceptors, epinephrine-induced contractile potency, susceptibility to phorbol ester (PDBu) modulation, and differences in membrane fluidity were studied in bovine aorta from young (3-8 weeks) and adult or mature (6-8 years) animals. Membranes prepared from aorta of adult animals exhibited a two-fold higher receptor density while [3H]prazosin affinity was unchanged. Epinephrine displacement studies revealed both high- and low-affinity binding in membranes from the aortas of young animals whereas, preparations from adult animals exhibited only a single class of low-affinity sites. In low-temperature binding studies, membranes prepared from aortas of adult animals exhibited both high- and low-affinity agonist binding, in proportions about equal to those of young animals. The ability of PDBu to uncouple alpha 1-adrenoceptor from G-protein interaction is demonstrable in young but not in adult animals which raises the possibility of prior phosphorylation of receptors in the latter tissues. Aortas from young animals showed increased contractile potency to epinephrine and, in addition, were significantly more fluid as compared to aortas from adult animals. Alterations in the membrane environment or phosphorylation state of the alpha 1-adrenoceptor may thus provide age-dependent modulation of its function.

Adrenergic alpha-Agonists↗
PubMed1990

Species differences in chlorethylclonidine antagonism at vascular alpha-1 adrenergic receptors.

Chloroethylclonidine (CEC) inhibition of norepinephrine-induced contractile response was studied in rat and rabbit aorta. CEC inhibition was irreversible, but displayed a competitive pattern characterized by rightward shifts of the norepinephrine EC50 with little or no decrease in maximum response. CEC appeared to shift response to a discrete but lower affinity state. The time course for irreversible inhibition by 10 microM CEC was faster for rat aorta (T1/2 = 18 min) than for rabbit aorta (T1/2 = 118 min) indicating a difference either in receptor occupation or in the rate of alkylation after occupation. Measurements of reversible CEC affinity in rabbit aorta yielded a pKB of 6.3 and the rate of alkylation was not significantly increased at 100 microM CEC so that lower occupation could not account for the difference. Pretreatment with phenoxybenzamine significantly increased the sensitivity of rabbit aorta to CEC indicating a role for receptor reserve in determining the extent of CEC inhibition. Membrane fluidity measured by diphenylhexatriene fluorescence was lower in rabbit than rat aorta; however, dimethylsulfoxide or ethanol failed to alter the rate of irreversible CEC inhibition in the rabbit. Protein kinase C activation with phorbol dibutyrate failed to alter CEC alkylation in rabbit aorta. WB 4101 [2-(2,6-dimethoxyphenoxyethyl)-aminomethyl-1,4-benzodioxane] affinity was higher in rabbit aorta (pKB = 8.9) than rat aorta (pKB = 8.3) consistent with a contribution of alpha-1A and alpha-1B adrenergic receptor subtypes to differences in CEC sensitivity, although the difference was not as great as would be predicted.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Antagonists↗
PubMed1990

Modulation of bovine aortic alpha-2 receptors by Na+, 5'-guanylylimidodiphosphate, amiloride and ethylisopropylamiloride: evidence for receptor G-protein precoupling.

The influence of Na+ and 5'-Guanylylimidodiphosphate [Gpp(NH)p] on [3H]rauwolscine binding to alpha-2 adrenergic receptors was studied in plasma membranes prepared from bovine aorta. Both Na+ and Gpp(NH)p increased [3H]rauwolscine affinity while maximal binding capacity (Bmax) was significantly increased only with Gpp(NH)p. The increase in affinity was solely due to an increase in the association rate, while dissociation rate was not altered. In contrast, Na+ and Gpp(NH)p each lowered the affinity of the agonist epinephrine for both high- and low-affinity binding sites. The effects of Na+ and Gpp(NH)p on agonist binding were additive, such that only in their combined presence was a homogeneous class of low-affinity sites observed. This indicates that alpha-2 receptor-guanine nucleotide-binding protein (G-protein) interactions are modulated by both Na+ and Gpp(NH)p but via different mechanisms. Amiloride (100 or 300 microM) and ethylisopropylamiloride (10 microM) produced dose-dependent reductions in [3H]rauwolscine affinity, and, in the case of amiloride, also reduced Bmax. Competition at the [3H]rauwolscine binding site as well as noncompetitive, allosteric effects were present. The presence of Na+ augmented the ability of amiloride to reduce Bmax, indicating a shared locus of action. These findings illustrate that vascular alpha-2 receptors can interact with G-proteins even in the absence of agonists (i.e., receptor/G-protein precoupling) and that Na+ ion concentration regulates this interaction. Amiloride can occupy a Na(+)-shared binding site, causing an allosterically induced loss of receptor binding, suggesting that ligand binding and G-protein binding depend upon common receptor features.

Amiloride↗
PubMed1990

Influence of amiloride derivatives on alpha-1 adrenergic receptor-induced contractions of the rabbit aorta.

Derivatives of amiloride that exhibit greater specificity for inhibition of either Na+/H+ or Na+/Ca(+)+ exchange were evaluated for their ability to influence phenylephrine (PE)-induced contractions of the rabbit aorta. Most, but not all, derivatives with alkyl substituents at the 5-amino position (which exhibit greater potency for Na+/H+ exchange inhibition) caused a dose-dependent contraction at concentrations above 10 microM. At higher concentrations and longer incubation times this contraction reached 70 to 80% of the maximal PE response. Contractions induced by 5-amino-substituted amiloride derivatives were dependent upon extracellular Ca(+)+ and were inhibited by either extracellular acidification or intracellular alkalinization. This suggests that they resulted from an influence of intracellular acidification on Ca(+)+ transport. Contractile responses to PE (1 microM) were reduced by most but not all 5-amino-substituted derivatives in conjunction with tension development. Dimethylamiloride, however, failed to cause a contraction at doses up to 100 microM but was the most potent inhibitor of PE-induced contractions among the 5-amino derivatives. Dose-response curves for PE were shifted both to the right and downward by increasing concentrations of amiloride, which indicates both competitive and noncompetitive types of inhibition. Guanidino-substituted derivatives such as benzobenzamil were the most potent antagonists, producing noncompetitive inhibition in excess of 90% at a concentration of 10 microM. The differing patterns of inhibition as well as the presence or absence of intrinsic contractile activity indicate that amiloride derivatives have the potential for multiple pathways of action that modify arterial contractility.

Amiloride↗
PubMed1989

Reduction of norepinephrine-induced tonic contraction and phosphoinositide turnover in arteries of spontaneously hypertensive rats. A possible role for protein kinase C.

Experiments were conducted to determine whether a difference in receptor-induced phosphatidylinositol hydrolysis occurred in aorta from spontaneously hypertensive rats (SHR) v Wistar-Kyoto (WKY) rats, and whether such a difference was correlated with contractile response. Basal incorporation of 32P into phosphatidylinositol (PI), phosphatidylinositol phosphate (PIP), phosphatidylinositol diphosphate (PIP2) and phosphatidic-acid (PA) was not different between SHR and WKY groups. However, after five minutes of norepinephrine (NE; 10 mumol) exposure, increases in 32P labeling were markedly lower in SHR arteries. The percentage decrease amounted to 45% for PI, 68% for PIP, 100% for PIP2 and 58% for PA. Basal incorporation of 3H-myo-inositol into inositol monophosphate (IP) was similar for SHR and WKY groups. However, after 30 minutes of NE (10 mumol), SHR arteries failed to show an increase in 3H-IP levels, whereas labeling was increased 219% in WKY arteries. The contractile response of SHR arteries to 10 mumol NE showed a marked reduction in the rate of development of the tonic phase that has previously been shown to be supported by activity of protein kinase C. Higher Ca2+ levels failed to augment the SHR response, whereas WKY responses were significantly increased. Contractions in the presence of the phorbol ester tetradecanoylphorbolacetate exhibited a similar reduction in NE-induced tonic phase tension. These results indicate an impairment in SHR arteries at the level of receptor-induced formation of inositol cycle second messengers, possibly due to elevated basal levels of protein kinase C. These differences may be important in explaining altered vascular responses in primary hypertension.

Animals↗
PubMed1989

Effects of intracellular alkalinization on resting and agonist-induced vascular tone.

To evaluate the influence of intracellular alkalinization on basal and agonist-induced vascular tone, we studied the effect of NH4Cl on rat aorta. NH4Cl induced a gradually developing contraction in a dose-dependent manner. Although the contractile response to 20 mM NH4Cl was associated with a latent period (LP) of 23.4 +/- 2.8 min, intracellular pH (pHi) measurements in cultured rat aortic smooth muscle cells showed that NH4Cl-induced intracellular alkalinization was immediate and transient, returning to basal pHi levels in about 30-35 min. Agents that elevate Ca2+, such as A23187 and high KCl, significantly reduced the LP associated with 20 mM NH4Cl-induced contraction. NH4Cl-induced contractions were sensitive to extracellular Ca2+ removal and to the addition of forskolin (1 microM); however, NH4Cl by itself did not cause Ca2+-influx as shown by 45Ca-uptake studies. Addition of 20 mM NH4Cl to precontracted tissues resulted in a transient relaxation, which was complete in approximately 10 min, followed by a contraction above the original level of tone. NH4Cl pretreatment caused time-dependent alterations in both the rapid and slow phases of phenylephrine and angiotensin II contractions. Rapid-phase of phenylephrine and angiotensin II contractions. Rapid-phase responses were diminished at shorter NH4Cl incubation times (10 min), whereas slow-phase response was augmented after a longer incubation (20 min). Overall, the vasorelaxant and vasoconstrictor effects induced by NH4Cl suggest a complex relationship between intracellular alkalinization and arterial contractility.

Acetates↗
PubMed1989

Influence of atrial natriuretic factor on 5-(N-ethyl-N-isopropyl)amiloride-sensitive 22Na+ uptake in rabbit aorta.

Because atrial natriuretic factor (Atriopeptin II, ANF) exerts potent effects on Na+ transport in a number of tissues, we examined its influence on 22Na+-uptake in isolated rabbit aorta segments and the possible relation to ANF-induced vasorelaxation. ANF increased 22Na+-uptake by 44% with an EC50 of 12 nM whereas sodium nitroprusside was without effect. The increase was blocked by the selective inhibitor of Na+/H+ exchange 5-(N-ethyl-N-isopropyl)amiloride (EIPA) but was not sensitive to the guanylate cyclase inhibitor LY 83583, indicating ANF-induced activation of Na+/H+ exchange via a cyclic GMP (cGMP) independent pathway. The ability of ANF to relax phenylephrine-induced contractions of rabbit aorta was inhibited by EIPA at concentrations which produced inhibition of Na+/H+ exchange whereas sodium nitroprusside-induced relaxation was only marginally affected. EIPA caused a 90% decrease in the ability of ANF to increase cGMP, but did not interfere with the sodium nitroprusside-induced increase. LY 83583 blocked the ability of ANF to increase cGMP formation but failed to reduce ANF-induced vasorelaxation. These results suggest that ANF activation of EIPA-sensitive 22Na+-uptake occurs before cGMP formation perhaps at the level of the ANF receptor itself. The vasorelaxant effects of ANF involve a significant cGMP-independent component which is EIPA sensitive.

Amiloride↗
PubMed1988

Influence of alpha 1-adrenergic receptor stimulation and phorbol esters on hepatic Na+/K+-ATPase activity.

The effects of the alpha 1-adrenergic agonist phenylephrine (PE) and the phorbol ester 4 beta-phorbolmyristate-acetate (PMA) on sodium pump function were studied in the rat liver. In order to distinguish between direct and indirect influences, ouabain-sensitive 86Rb uptake by intact liver slices was compared with ouabain-sensitive Na+/K+-ATPase activity in plasma membranes isolated from PE and PMA-perfused livers. At a buffer Ca2+ level of 2.5 mmol/l, PE (10 mumol/l) caused an initial stimulation of both 86Rb uptake and Na+/K+-ATPase activity followed at 5 min by a decrease in both activities. Both actions were blocked by the alpha 1-antagonist prazosin. The decrease in ouabain-sensitive Na+/K+-ATPase was paralleled by an increase in Mg2+ ATPase activity. At a Ca2+ level of 1.5 mmol/l, PE stimulation of 86Rb uptake and Na+/K+-ATPase was sustained, and the inhibitory component was not expressed. PMA (4 mumol/l) reduced 86Rb uptake and Na+/K+-ATPase and similar to PE, this inhibition was paralleled by an increase of Mg2+-ATPase activity. 4 alpha-PMA, which does not activate protein kinase C, failed to influence 86Rb uptake or Na+/K+-ATPase. These results demonstrate that PE and PMA effects on ouabain-sensitive 86Rb uptake are preserved in isolated membranes, indicating a direct influence on the Na+/K+-ATPase. A role for protein kinase C in modulating sodium pump activity is suggested.

Adrenergic alpha-Agonists↗
PubMed1988

Phorbol ester-induced modulation of agonist binding to alpha-1 adrenergic receptors in bovine aortic membranes.

Effects of the protein kinase C-activating phorbol ester, phorbol dibutyrate (PDBu) on the binding behavior of the alpha-1 adrenergic receptor were determined from radioligand binding assays at 25 and 2 degrees C. Membranes prepared from PDBu-treated bovine aorta exhibited a 16% reduction in [3H]prazosin binding capacity, whereas [3H]prazosin affinity was unchanged. This may reflect a role for protein kinase C-mediated receptor phosphorylation in determining receptor turnover and surface density. After PDBu treatment, the affinity of epinephrine for [3H]prazosin sites was altered in two respects. Control membranes exhibited both high and low affinity epinephrine binding (KDH, 20 nM; KDL, 1086 nM) whereas, PDBu-treated membranes exhibited only a single class of low affinity sites (KDL, 655 nM). The inclusion of 5'-guanylylimidodiphosphate caused the loss of high affinity sites in control membranes but had no effect on PDBu-treated membranes (KDL, 681 nM). Thus, protein kinase C blocks the ability of the agonist-receptor complex to couple to a GTP binding regulatory protein. In binding studies conducted at 2 degrees C epinephrine also bound to high (KDH, 34 nM) and low affinity (KDL, 1920 nM) sites although the percentage of high affinity sites was higher (percentage of RH, 80) than at 25 degrees C (percentage of RH, 19). PDBu-treated membranes also exhibited two agonist affinity states in 2 degrees C studies although affinity was slightly reduced (KDH, 74 nM; KDL, 2405 nM). 5'-Guanylylimidodiphosphate was without effect at 2 degrees C. These results indicate that a high affinity agonist binding state can still be achieved after PDBu treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Agonists↗
PubMed1987

Protein kinase C-mediated intracellular alkalinization in rat and rabbit aortic smooth muscle cells.

The influence of protein kinase C (C-kinase) activation on intracellular pH (pHi) of cultured rat (RASM) and rabbit (RBASM) aortic smooth muscle cells was studied by employing a pH-sensitive fluorescent-dye 2,7-biscarboxyethyl-5,6-carboxyfluorescein (BCECF). The known C-kinase activators 12-O-tetradecanoylphorbol-13-acetate (TPA), phorbol 12,13-dibutyrate (PDBu) and mezerine as well as the agonist angiotensin II each caused an intracellular alkalinization of approximately 0.1-0.15 pH units in RASM and RBASM cells grown in serum-free conditions. TPA-induced alkalinization was sensitive to the Na+/H+ exchange blockers amiloride and 5-N-ethylisopropyl-amiloride (EIPA). These results suggest that protein kinase C activation leads to intracellular alkalinization in vascular smooth muscle cells and the increase in pHi might play an important role in receptor-coupled arterial contraction.

Amiloride↗
PubMed1987

Influence of furosemide on rubidium-86 uptake and alpha-adrenergic responsiveness of arterial smooth muscle.

Furosemide-induced inhibition of 86Rb uptake was measured in rat and rabbit aorta and compared with its ability to inhibit contractions induced by alpha-adrenergic agonists. In both rat and rabbit tissues, furosemide defined a portion of 86Rb uptake (IC50 = 2.5 microM) which was distinct from the ouabain-sensitive fraction. Furosemide-sensitive 86Rb uptake was [Cl-]ext dependent and required Na+ and K+ for optimal activity, suggesting that it reflected a Na+-K+ cotransport process. Furosemide-sensitive 86Rb uptake was found to be greater in HEPES buffer than in bicarbonate buffer. Phenylephrine-induced contractions of rat and rabbit aorta were inhibited by furosemide; however, rat responses were far more sensitive. Agonist-induced uptake of 45Ca was reduced by furosemide in rat aorta, but not in rabbit aorta. Agonist-induced 45Ca efflux stimulation was reduced in both species. These findings indicate the presence in arteries of a furosemide-sensitive, Cl-dependent Na+-K+ cotransport process. Along with other monovalent transport processes, it may modulate Ca2+ availability and thereby influence arterial contractility.

Animals↗
PubMed1987

Alpha-1 adrenergic coupling events induced by full and partial agonists in rabbit aorta.

Differences in the ability of full vs. partial agonists to initiate alpha-1 adrenergic receptor-mediated coupling events were studied in isolated segments of rabbit aorta. Mono- and dimethoxysubstituted tolazolines produced contractile responses which, at their maximum, were 27 to 100% of the response produced by the full agonist phenylephrine. In addition to differences in maximum response, contraction kinetics varied between full and partial agonists. Responses to partial agonists displayed a slower approach to peak tension and loss of the rapid phase of tension development which is associated with release of intracellular Ca++. Among the tolazoline series 3,5 dimethoxy-, 3 methoxy-, and 2 methoxy derivatives were compared further with phenylephrine for their ability to cause phosphatidylinositol cycle turnover, intracellular Ca++ release and Ca++ influx. For each of these coupling events, a rank of phenylephrine greater than or equal to 3, 5 greater than 3 greater than 2 was observed. However, a higher percentage of Ca++ influx vs. Ca++ release was observed for the partial agonists, suggesting that their contractile responses may be more dependent upon extracellular Ca++ than intracellular Ca++. Our results indicate that partial agonists initiate the same coupling events as full agonists; however, the relative proportion of Ca++ release and influx may be different for partial agonists because of the reduced rate of second messenger production.

Adrenergic alpha-Agonists↗
PubMed1987

Different affinity states of alpha-1 adrenergic receptors defined by agonists and antagonists in bovine aorta plasma membranes.

Evidence for a nonlinear relationship between alpha-1 adrenergic receptor occupancy and tissue responses, together with the finding of different affinity states for agonist binding, has raised the possibility of functional heterogeneity of alpha-1 adrenergic receptors. We have conducted studies to examine: 1) binding characteristics of [3H]prazosin, 2) competition of antagonists at these sites and 3) different affinity states of the receptor for agonists and modulation of these states by 5'-guanylylimidodiphosphate [Gpp(NH)p]. A plasma membrane-enriched vesicular fraction (F2; 15%/33% sucrose interphase) was prepared from the muscular medial layer of bovine thoracic aorta. [3H]Prazosin binding was characterized by a monophasic saturation isotherm (KD = 0.116 nM, Bmax = 112 fmol/mg of protein). Antagonist displacement studies yielded a relative potency order of prazosin greater than or equal to WB4104 much greater than phentolamine greater than corynanthine greater than yohimbine greater than or equal to idazoxan greater than rauwolscine. Competition curves for unlabeled prazosin, WB4101 (2-(2,6-dimethoxyphenoxyethyl)-aminomethyl-1,4 benzodioxane) and phentolamine were shallow and were best modeled to two binding sites with picomolar and nanomolar KD values. Gpp(NH)p was without effect on antagonist affinity. Agonist (epinephrine, norepinephrine and phenylephrine) competition with [3H]prazosin binding was biphasic with pseudo-Hill slopes less than 1.0. Binding was best described by a two-site model in which the average contribution of high affinity sites was 23% of total binding. KD values for the high affinity site ranged from 2.9 to 18 nM, and 3.9 to 5.0 microM for the low affinity site.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Agonists↗
PubMed1986

Differences in phospholipid incorporation of 32P relevant to alpha 1-receptor coupling events in rat and rabbit aorta.

Labelling of membrane phospholipids with 32P was compared in rat and rabbit aorta under basal conditions and during alpha 1-receptor stimulation. Incorporation of 32P proceeded at a significantly higher rate in rat tissue. The ratio of basal labelling following 30 min of incubation for rat/rabbit arteries was 4.8 for phosphatidylinositol diphosphate (PIP2), 6.0 for phosphatidylinositol phosphate (PIP), 9.0 for phosphatidylinositol (PI), 6.0 for phosphatidic acid (PA) and 18.7 for phosphatidylcholine (PC). Addition of 10(-5)M norepinephrine (NE) to labelled tissues resulted in a similar decrease in [32P]-PIP2 in both rat and rabbit tissues. Greater percent increases were seen in rabbit tissue of [32P]-PA (4-6 fold), and [32P]-PI (3-5 fold), when measured over the initial 10 minutes of agonist exposure. While NE caused a gradual increase of 32P incorporation into PC in rabbit aorta, reaching 180% above control after 10 minutes, PC labelling was not increased in rat aorta. Our findings provide evidence for the enhanced labelling of rat vs rabbit aorta phospholipids. This may account for differences in receptor responses and associated Ca+ movements which have been previously recognized to exist between aorta of these two species.

Animals↗
PubMed1986

Acute desensitization to angiotensin II: evidence for a requirement of agonist-induced diacylglycerol production during tonic contraction of rat aorta.

A possible role for protein kinase C during the tonic phase of arterial contraction was examined in rat aorta by observing the effects of the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), on angiotensin II (AII)-induced responses. The ability of AII and phenylephrine (PE) to induce diacylglycerol (DAG) production was monitored as agonist-stimulated 32P-labelling of phosphatidic acid (PA). AII (5 X 10(-7) M) causes only a transient contractile response, while PE (10(-5) M) causes a sustained tonic contraction. 32P-labelling studies showed that AII caused an initial increase of PA synthesis equal to PE, however, AII failed to sustain this increase at 5 and 10 min while PE was able to do so. This indicates a failure of AII to provide DAG to sustain protein kinase C activation. Activation of protein kinase C with TPA prior to and during AII exposure converted the normally transient contraction to a more sustained, tonic pattern. These results suggest that the capacity of neuroendocrine agonists to maintain tension is due to their ability to produce DAG continuously and thereby activate protein kinase C.

Angiotensin II↗